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Why do Airbus sidesticks add their inputs?
There have been a couple of Airbus disasters where, in the confusion leading up to the crash, both pilots have attempted to control the aircraft with their sidesticks at the same time. In the absence of either pilot using the priority button, the effect of this is that both inputs are added, and the result clamped to the maximum single input.
On the face of it, this is a very curious design decision. Obvious alternatives include prioritising the left-seat stick (unless the priority button is used), or even averaging (instead of summing) the inputs.
Are the original reasons for this design decision documented? Is there an advantage to summing the inputs?

average would work exactly as sum&clamp because you want each single pilot to input the max deflection

@ratchetfreak: If both pilots are inputting 75%, the average is 75%, but sum-and-clamp gives 150% clamped to 100%.

but you want 50% average to be full deflection in case one pilot is following a checklist while the other is focusing on flying

I also thought this was an odd way of doing things while reading about AF447. It seems like it should be the same way pilots are taught in CRM where you make it clear who is PF and have the stick only accept input from that side. If you hand over control then the other pilot hits the priority button.

@ratchetfreak This only applies when both controls are deflected from the centre, so if one pilot applies full deflection while the other has his hand off the stick, you get full deflection.

@dan than what about when the other pilot wants to take over or bumps the stick? suddenly the input snaps back to 50%

@ratchetfreak Summing is also a problem if you hand over while the stick is partly deflected. The only way to hand over smoothly (other than with the stick central) is to use the priority buttons.

@Dan, it still makes more sense than switching to average on dual input. Essentially, nothing makes sense. Dual input is an invalid use. But the system must do something, and taking sum is easiest, consistent and no worse than any of the other bad options.

I believe that there is some logic in the design, actually, even if I don't really fancy it. If you think of the traditional yoke as a control element where a certain force (or moment, rather...) results in a certain change of flight path, then if both pilots apply the same force (rather than targeting the same deflection), the resulting aircraft reaction is more pronounced than if only one pilot applies that force, although probably not with linear relation. The sidestick controlled flight control system does the same.
What is missing much more, to my mind, is feedback to one pilot about what the other one is doing with the stick. I believe that having them interconnected or back driven would probably not have been such a bad idea.

+1 couldn't agree more on the feedback and interconnection. For me, safety is another reason, so that any pilot will have full control authority if the other is not touching the stick, without pressing the priority switch first.

+1 for a good reasoned explanation, but I'm still holding out for a non-speculative answer.

This was my thought as I was reading the question!

@DanHulme Can we conclude with the community answers as: no one understands why Airbus adds their inputs?

Why do Airbus sidesticks add their inputs? I do not work for Airbus and am not privy to their design documents, but here is what I reckon based on the over 50 real-time simulation models of aircraft flying controls I've written and tuned:

Summing the outputs makes most sense in avoiding discontinuities in position input, and provides the greatest flexibility if only one pilot at a time handles their side stick. A stick in centered position gives zero output. If a pilot transfers control to the other pilot, and no priority button is pressed, the flight control inputs from the two sticks have no discontinuity. Input from any pilot plus zero input from the other pilot works both ways, regardless of priority button status.
Only one pilot at a time should operate their side stick. If the non-operating pilot does provide a stick input, summing the two outputs results in a change in attitude that alerts the PF of the action of the other pilot. Averaging the inputs would do this to a much lesser amount, or not at all. Giving priority to left stick may be counterproductive: what if the captain has a heart attack while the FO is flying?

As long as proper procedure is followed and only one pilot at a time handles a stick, summing the outputs works best. However the situation breaks down when proper procedure is not followed: in times of emergency and urgency, in the absence of clear heads. Two pilots each continue to provide very different stick outputs - which one should the aircraft use? How can it make a decision of which of the two inputs is the valid one, if the humans have not instructed it? There is no fool proof solution to this, so picking the best solution when procedure is followed (summing the outputs) makes sense and provides flexibility and continuity.

There have been a couple of Airbus disasters where, in the confusion
  leading up to the crash, both pilots have attempted to control the
  aircraft with their sidesticks at the same time.

Picture source
Consider the case of QZ8501. The captain is an ex military pilot, recognises the stall and provides proper recovery input to the stick. Had he instructed the FO to not touch the stick, he might have recovered successfully. But his ambiguous use of English (not his first language) caused the FO to follow perceived instructions and give a pull up input, of which the captain was unaware.
Summing the stick outputs did not save them, nor would have averaging the outputs. Transferring authority to the captain would have in this case, but now we would be waiting for Murphy's law: the captain panics while the FO gives proper inputs. I've heard anecdotal evidence of a case just like that, in gusty conditions at landing with an FO highly experienced in bad weather while the captain was from a warm and sunny country.
The basis of your question is a situation where proper procedure is not followed due to an emergency, and in this situation none of the options work very well. The only real solution here is to couple the sticks, and provide one output as a result of conflicting force inputs, like in physics. If there is no time for the rational brain to act, the only solution is to make use of the rapidly reacting sensory organs built into all humans.

I cannot see how this is an answer; it should be a comment.

The question, as asked, can only be answered by someone from the OEM who was involved in the design decision. It is a question about design, introduces various options and critiques the one chosen. The first answer starts with I believe. I've written my answer based on what I've seen in my experience with flying controls, civil amd military, fixed wing and rotary wing.. The BEA mentioned the lack of feedback to the pilots as a contributing factor to AF447: we're talking about a lack of feedback here, of what the other side is doing, in a highly stressed situation.

Yes, but you don't even attempt to answer the question that was asked, even via speculation. You talk about a somewhat related aspect of it, but it really isn't an answer to the question, which is what our site is designed around.

The question was: "Why do Airbus sidesticks add their inputs?" My answer is: to get around a fundamental flaw in the design. Bit it isn't a good workaroumd, as the OP mentions as well.

Have added a picture that may illustrate my answer.

@kevin how is it now?

I think it's a lot worse now. There's one paragraph that addresses the question and then four paragraphs of preaching about coupled inputs.

@Dan yes I get a bit carried away sometimes, was trying to illustrate the argument. I did not realise that I might have offended you by mentioning that coupling of the stick wasn't listed as an option. Oh well. Any thoughts on the answer paragraph?

@Koyovis I'm not offended; I'm just not interested. The Airbus vs. Boeing design philosophy question is a much bigger one than I want to face. I think your relevant paragraph is hinting at something that Jan Hudec mentioned in the comments: that it's useful to avoid the result jumping when a second pilot starts manipulating their stick. Even so, I'm still hoping that someone can quote an official publication by Airbus, or an interview, or similar, describing their actual rationale.

@DanHulme, I understand, apologies for the rant but that is the way I feel about the one Airbus design decision I cannot understand. However, given that the sticks are uncoupled, they've chosen the most versatile solution that always works if only one pilot handles a side stick, regardless of override button status All the best with the quest.

"always works if only one pilot handles a side stick" I'll say again what I mentioned in a comment: the summing rule only applies when both controls are not centred. In that case, any way of combining the inputs would still work if only one pilot handles a stick.

@Dan "In that case, any way of combining the inputs would still work if only one pilot handles a stick". I'll say again what I mentioned in my answer but I'll attempt to improve the phrasing: summing the outputs is the only way to prevent a discontinuity in the total output - a centered stick has an output of zero.

@Koyovis Agreed, and I think the point about the discontinuity could be stressed more, as it's a big advantage of summing over averaging, but it's only an advantage when both pilots use their sticks at once.

A complete re-write with less of a rant. A bit lengthy though.

The first four paragraphs of this answer are excellent.

This will be a theoretical answer, but unless the site is visited by someone from the Airbus control design team, that is probably the best we are going to get. Let me list for you the extremely desirable characteristics of the 'sum' approach.

In the normal modes of operation, i.e. when one pilot is 'hands on' and the other 'hands off', the sum function means that the controls behave exactly like the pilots expect them to. I cannot emphasize how important this characteristic is. More importantly there isn't any switching' or 'special case' involved. More will be said on this absence of 'special case' later.
It's suggested in the question that the inputs be 'averaged' instead of summed. However this means that a pilot attempting to fly the plane under normal circumstances gets only half the input he expects - full deflection of the stick gets only half deflection of the controls (because the other stick is centred). This is obviously completely unacceptable, and means that we would need either to always use the priority buttons, or to detect that the other stick is centred as a 'special case'. The reasons why this is a bad idea will be explained below.
The 'special case' approach, where the stick behaves normally if the other stick is centred, but averages with the other stick if it is not, introduces some potentially catastrophic problems. If the 'centred' stick were to be moved very slightly - perhaps because the non-flying pilot accidentally brushed it with his sleeve, or there was a bump of turbulence - then the mode would switch. The response of the controls would suddenly change from the input requested by the flying pilot, to half that input (average of the flying pilot's input with the almost-centred other stick). A sudden large change of control position as a result of a tiny change like that is absolutely unacceptable, and under some circumstances might be life-threatening.
The other advantage of the 'sum' approach is that any move of each stick always produces a similar response in the plane, no matter what the other pilot is doing. A certain deflection of the stick always produces approximately the same control response, whether or not the other pilot is also using the controls. This is extremely important. To have the controls respond differently depending on what the other pilot is doing has the potential to be extremely confusing.
The 'averaging' function (proposed in the question) makes it impossible for one pilot to get full deflection of the controls when both sticks are active. Both pilots' maximum input are required (unless the 'priority' button is used - more later on why that is a bad idea). In the scenario where the non-flying pilot sees an emergency situation that immediately requires maximum control input, anything that prevents his ability to do that is life-threatening.
The 'sum' function allows one pilot to make minor corrections to the other pilot's input. For example, if the First officer is flying, and is keeping the nose slightly too low, the captain can correct by making a small control input. As we saw above, if the 'averaging with mode switch' approach is taken, then the captain's input would result in a large response from the aircraft, not the small one he wants.
It may be argued that alternative modes can work if the 'priority' switch is always used. However this requires that the button be pressed everyone time a pilot takes or gives control. Introducing an additional action - even one as simple as pushing a button - into an already well-established procedure is going to be dangerous. No other planes require you to push a button to gain control, and in a crisis it is likely that the additional action will be omitted. When a pilot-not-flying suddenly sees another plane on a collision course, or sees that the pilot flying has collapsed, their reaction will be to move the controls immediately - not to push a button and then manipulate the controls. On every other plane they have flown this action will have worked. The cost of that difference could be measured in lives lost.
The idea that the left seat be favoured if the priority button is not used is also very problematic. Airliners are flown nearly 50% of the time from the right seat. The priority button would have to be used 50% of the time. The problems with the priority button would still be there, although admittedly half as often. The only certain way to make a control input in an emergency would still be to push the priority button (with the problems we listed above), unless you went through the additional step of thinking 'which seat am I in and do I have to push the button?", a step which would only slow response, with potentially catastrophic results.


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Why is extreme cold weather a challenge at airports, since jets operate at extreme cold conditions in flight?
Wondering what specifically the issues are. Obviously, taking off and landing have more 'moving parts' but more curious about the actual extreme cold.
I assume the operating temperatures at cruise are much lower than ground temps.

For landing, the altimeters are affected at very low temperatures. The altimeter will indicate a higher altitude than actual.

The extreme cold is not an issue so much as the weather that typically accompanies it and the fact that planes are not always designed to be started in extreme cold with out some assistance even if they can run in it. For example so long as the weather is good and the aircraft are equipped, there are plenty of airports in Antarctica
When extreme cold is accompanied by precipitation you can get ice build up on the runway which is quite dangerous. Most airports that are in an area of regular cold weather are equipped in some way to handle this.
Extreme cold temperature that comes with/because of frontal movement may also come with very high winds that can exceed aircraft limits. But high winds can come with warm weather as well so this is not exclusive to the cold.
For piston engines you have an issue of thick oil. When the temperature drops the oil thickens and it becomes hard to start the engine as well as running the risk of engine damage. Piston engines in commercial operations are much less common than they once were so this is less of an issue. However the general aviation fleet is still pretty effected by this issue.
Jet engines do have cold start procedures just like piston engines, there is a good discussion on that here. You can see a neat video of an A320 starting up in -28C conditions here so cold weather starts are not a huge issue.
Most airports have some form of ground crew that operate in the elements. Crew like baggage handlers, aircraft marshaller, and even mechanics may work out on the ramp to get an aircraft loaded and ready to go. This is one instance where sheer cold can be a factor although weather can also make working conditions very tough, even if proper protective gear is available.

On the design side, transport aircraft are certified for a minimum operating temperature, typically -40C, sometimes -45 or maybe -50, and this will be a basic operating limitation, but only for departure purposes as it will regularly see -70 at high altitudes in the winter in the north.
This means that an airplane certified to -40 will not be able to legally depart an airport with an SAT of -45 and will have to wait around for the temperature to warm up.  This happens in the arctic quite a bit.
Operating components are also certified to the airplane's minimum temperature limitation and will have to perform to the required standard in endurance and qualification testing only to that minimum temperature, not the temperature it might be exposed to at altitude.  This can cause problems for mechanical non-hydraulic components away from the fuselage, like screwjack flap actuators(hydraulic components get warmed by the fluid and never really get cold soaked).  In theory, if you tried to deploy flaps at 35000 ft at -65, chances are they won't come out because the grease or oil in the gearbox is congealing.
However, this isn't the problem it seems because when the flaps are called for, the airplane is back down to somewhere around 3000 ft agl and components have warmed up at least to their min cert temp and can be expected to work.

At cruise levels, the air holds nearly no water vapor and therefore the problems of icing & snow are less likely to occur than on ground.
Also, with already running engines, there is heat available to keep even with low outside temperature parts of the aircraft heated, e.g. the wing edges as anti-ice measures. I don't know the details about jet engines enough, but it might be, that they have a narrower temperature range for startup than for cruise settings. So it might be okay to run an engine at -20°C but not to start it at this temperature - but that's something hopefully others will know better and write a more detailed answer about that.

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Sustainable aircraft technologies
I'm a student starting a research project on sustainable aircraft technologies. I've been particularly interested by distributed electric propulsion (DEP), which is currently being tested by NASA with the X-57 Maxwell (I'm thinking the added efficiency of DEP combined with progress in battery technology could eventually make electric flight a more feasible option). My supervisor has also pointed me to ion drives. Are there any other technologies in development that I should be aware of? Information on progress, potential, who is developing the technology, as well as links to scholarly articles are all appreciated.

The world seems to have quite a narrow perspective on "sustainability" these days, its all electricity and batteries... I hope you are rigorous in your research, taking into account the vast progress in "traditional" engine tech combined with renewable biofuels. Batteries are really quite far from being truly sustainable option in aviation as they have a horrible energy density. I personally swear by liquid fuels, but I do firmly believe some sort of hybrid solution will eventually conquer air travel.

Not to mention the environmental devastation of battery production and disposal.

Thanks for the quick responses! Biofuels do seem like a promising avenue. My only concern is that combustion, even of fuels from alternative sources, would still contribute to rising carbon dioxide concentrations and climate change (the transportation industry, and aviation in particular, is one of the world's largest emitters). Do you know of any liquid fuels that do not produce greenhouse gases? (Aside from liquid hydrogen; from what I've heard it doesn't look too promising.)

You might also consider evaluating Hydrogen-powered aircraft and Biofuel as ways to operate aircraft with combustion engines on alternative fuels that can be produced in a more sustainable manner.

Thanks for the quick response! I responded to this to some degree in a comment on the question, feel free to continue the thread.

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What qualifies for "mass disseminated data" for an abbreviated briefing?
I'm reading about the different types of pre-flight briefings you can get and in the section for Abbreviated Briefing (AIM 7-1-4c) is mentions the phrase "mass disseminated data".

Request an Abbreviated Briefing when you need information to supplement mass disseminated data...

Is there a particular definition or list of what qualifies for "mass disseminated data"? I often use aviationweather.gov to get a good overview of what's going on before a flight. Does that qualify?

If you look a page or two earlier in the AIM in section 7-1-5(b) the FAA gives two examples:

b. Standard Briefing. You should request a Standard Briefing any time you are planning a flight and you have not received a previous
  briefing or have not received preliminary information through mass
  dissemination media; for example, TIBS, TWEB (Alaska only), etc.

That's interesting because TIBS was just discontinued (yesterday!) and TWEB is only in Alaska  (weather.gov says it's in other states too but that appears to be out of date according to the FAA's procedures). I have no idea what they include in "etc."
Personally, until I looked into this question I always assumed that "mass disseminated media" meant your local TV station's weather reports :-)

I don't know if there is a particular list.
I would consider sources like the AVIATION WEATHER CENTER which you linked to, skyvector.com, foreflight.com, 1800wxbrief.com, even intellicast.com, all to be mass disseminated data.  I look at all those too, and then just ask for an Abbreviated briefing when I'm making a short local hop between airports I'm familiar with to make sure I get any TFRs and NOTAMs that may have popped up recently.


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Does a hold-entry count as a hold for instrument currency?
So in looking at the instrument currency requirements for the FAA (6 approaches, holds, intercepting & tracking courses), I'm having difficulty nailing down what constitutes a hold.
Based on AIM 5-4-9(a)(5) where it talks about HILPT, it sounds like all I need is to do the hold-entry and get established inbound, which feels a bit odd since for a parallel-entry since that's nearly equivalent to a procedure turn (which I believe wouldn't count as a hold).

The holding pattern maneuver is completed when the aircraft is established on the inbound course after executing the appropriate entry.

Based on the above, I assume if I fly a HILPT as part of an approach in actual/simulated instrument conditions, I can count that as a hold. Following that logic, would flying the hold-entry at a missed approach fix also qualify as flying a hold? Or does that excerpt above only apply to a HILPT?
Is there any official guidance/interpretation provided in regards to this?

The entry of a hold is sufficient for the holding procedures task on the instrument rating practical test in the US and for execution of an instrument approach procedure that begins with a hold, so it follows that it would also be the appropriate standard of completion for currency purposes regarding the required holding procedure.
I think the text you quoted in the question serves as a sufficient source by itself.

Think about it this way: when do you report established in the hold?
Short answer: there isn't a clear definition of what "established" means with respect to a hold.  One reports entering the hold upon crossing the fix that defines the hold.
14 CFR 61.57(c)(1)(ii) simply requires "Holding procedures and tasks."  It does not specify which part, if any, of a hold is required.
For the sake of proficiency (or recency of experience, which is not necessarily the same as proficiency), which is the intent and purpose of 61.57(c), one should consider the elements of holding and procedures that are important.  Holding isn't possible unless one can correctly identify the hold and determine how to enter it.  Making the entry correctly (speed, altitude, correct direction of turns, establishing on the correct inbound course and on the protected side of the hold) is important, because that's the foundation of remaining in the hold, and in the case of a hold in lieu of a procedure turn, it's the essence of the entry to the approach procedure.  This is basic to any holding procedure, and should be considered when seeking proficiency and currency.  Most instructors will at least want to see a student or someone seeking an instrument proficiency check complete the hold entry back to the fix.
Since 1992, the FAA has held that for an approach to be counted for recency of experience, it must be conducted to minimums.  One cannot simply fly the beginning of the approach, and count it for recency of experience.  No such interpretation has been provided for holding procedures.  A conservative rendering of the regulation, which does not specify the extend of the holding procedure that must be completed, would be to execute the full hold.  If one is only doing a hold every six months, then doing at least a full hold isn't a lot to ask.
In context of the thread, by the time one has completed the entry and established on the inbound course to the fix defining the hold (for a hold in lieu of a procedure turn), one is certainly established inbound, and if cleared for the approach prior to crossing the fix (and if configured and ready for the approach), one has met the requirements to reverse course and become established.  One might not get a full turn in the hold, yet has performed "holding procedures and tasks."
https://www.ecfr.gov/cgi-bin/text-idx?SID=c6ecc972f33f3035f9c7b284d1e9cff9&mc=true&node=se14.2.61_157&rgn=div8

"...Since 1992, the FAA has held that for an approach to be counted for recency of experience, it must be conducted to minimums. " Actually, according to this FAA 2015 interpretation, IAP can be logged (even if you transition to VMC prior to MDA/DH), as long as you complete the Initial, Intermediate segments and are established on the final segment. See https://www.faa.gov/sites/faa.gov/files/other_visit/aviation_industry/airline_operators/airline_safety/InFO15012.pdf

The quote from @PaulCarew's link: A pilot may log an IAP for currency or training when the pilot accomplishes the IAP in accordance with the following conditions: ...
When conducted in an aircraft maneuvering in IMC, and the aircraft transitions from IMC to visual flight conditions on the final approach segment of the IAP prior to or upon reaching MDA or DA/DH

I'm sure someone may have a more specific answer, but I would simply consider an entry and one lap (back to the fix) as a loggable hold. I wouldn't personally log less than one lap because I didn't really practice the technique, timing, and protected side management that completing an entire lap entails.


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Stall speed requirement
I calculated my stall speed at 22m/s.
For this stall speed, would it be a better idea to increase it to use in my calculations later on or leave it as it is?
I thought increase it a little to be on the safe side so that my other calculations are safer estimates?

Theory is never truth if you don't check your result in reality.

In theory, there is no difference between theory and practice. In practice, there is...

You should use 23.459.

You stick with your stall speed but add a safety factor to all speeds which are multiples of it. In most cases this has already been done for you, for example when takeoff requires 1.3$\times$stall speed to be reached to calculate take-off distance.


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What’s the horizontal and vertical tail airfoil and volume of 747-400?
What’s the horizontal tail volume coefficient of 747-400? What’s the vertical tail volume coefficient of 747-400? What’s the horizontal tail airfoil of 747-400? What’s the vertical tail airfoil of 747-400?
How can I find these specifications? I can’t find it anywhere. Is it some sort of calculation I’m supposed to make??

"Is it some sort of calculation I’m supposed to make??" - how could we know? You've given no context, no hint of why you want this information. If it's possible that you need to calculate a value, giving us the information you have, and the reason why you need an answer might help us to help you make that calculation.

Have voted to keep the question open. The data asked for is very much related, and presented in a.o. in tables in a pre-design book,

This sort of data is incorporated in the aeroplane pre-design textbooks. The one I have is Synthesis of Subsonic Airplane Design by Torenbeek, which unfortunately predates the B747-400. But there is data available for the B747-100/200, in sections 9.5 9 Preliminary Design of the Horizontal Tailplane and 9.6 Design of the Vertical Tailpllane.
Table 9-2 lists a.o. the following parameters for the B747 100/200 horizontal tailplane:

Area fraction S$_h$/S = 0.267
Aspect ratio A$_h$ = 3.60
Taper ratio $\lambda_h$ = 0.264
Sweep angle $\Lambda_h$ = 37°
Tail volume fraction S$_h$l$_h$/(S$\bar{c})$ = 1.000

And from table 9-3 the data for the vertical tailplane:

Area fraction S$_v$/S = 0.196
Aspect ratio A$_v$ = 1.38
Sweep angle $\Lambda_v$ = 44°
Tail volume fraction S$_v$l$_v$/(S$\cdot$ b) = 0.0990

Airfoil sections for other aeroplanes of the era are listed in the table, also referenced in this answer, but not for the B747. Profile type must have been a closely guarded secret at the time already.

You can calculate the said coefficients after you google the needed dimensions for 747-400.
From EAA chapter 62 website "How Big The Tail by Stan Hall:

The Tail Volume Coefficients relate the area of the surface, the distance that area is from the aircraft's c.g., the wing area, the mean aerodynamic wing chord and the wing span.

In equation form Horizontal Tail Volume Coefficient (VH) looks like this.
VH = SH x LH / SW x m.a.c.
where SH = horizontal tail area, LH = distance from tail's aerodynamic center (more of which later) to the aircraft c.g., SW = wing area and m.a.c = the mean aerodynamic chord (more of this later, too)

For the Vertical Tail Volume Coefficient (VV) the equation looks like this.
VV = SV x LV / SW x b
where SV = vertical tail area, LV = distance from the vertical tail's aerodynamic center to the aircraft c.g., SW = wing area and b = wing span.


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FAA Approach and Landing (AL) numbers
I was trying to get a list of all ILS approaches in the US, which brought me to the FAA Aeronautical Product Release API to retrieve all the DTPP (Digital-Terminal Procedures Publication) as five zip files.
I noticed the naming conventions of the files began with a five digit number (left padded with zeros). For instance, SEA ILS RW 16C (CAT II & III) had the name: 00582I16CC2_3.PDF
Although it is easy enough to parse out the remainder of the name (I for ILS, 16 is the RWY, ...), it was this five digit number I was most interested in.
Previously, I happened to noticed that all approaches at a single airport had the same AL number at the top of the approach (at the time, I didn't even know what AL stood for). See the top margin:

Aeronautical Chart Users' Guide
I went to the Aeronautical Chart Users' Guide and found in the Section Instrument Approach Procedure Chart under U.S. Terminal Procedures Publication (p.98 on 2/23/24) some information:

At the center of the top margin is the FAA numbering system. This Approach and Landing (AL) number is followed by the organization responsible for the procedure in parentheses, e.g., AL-18 (FAA). Military procedures do no show an AL number, but do show the appropriate authority for the procedure, e.g., (USAF).

My questions:

Where can I find the mapping of Approach and Landing numbers to "organization responsible for the procedure in parentheses"?

Are these "organization's" just airports? Or might it include something that aggregates multiple airports in disparate locations?

Does anyone know where to find the document that would describe the DTPP naming convention?

Thanks

00582 in 00582I16CC2_3.PDF is the airport code in the metafile for the approach places.   On the D-TPP website, you can find an XML file in the 'E' download ZIP file that will map the procedure to the file.  These files are used by many companies to provide charts to users.  i.e. Foreflight, FltPlan Go, etc.
You can also download the metafile XML file separately from the bottom of this website.
https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/dtpp/search/

In the metafile, you can search for <alnum="582"> and you will find the XML data for Seattle Tacoma Washington Airport KSEA.
<airport_name ID="SEATTLE-TACOMA INTL" military="N" apt_ident="SEA" icao_ident="KSEA" alnum="582">

UPDATE
I assumed the airports database "SITE_NO" is the same as the AL numbering system on the approach plates.  The SITE_NO value for KSEA is 26395 and it is not the AL NUM.  It is interesting to dig into the data freely given by the FAA though.
If you want to dig into the data a little more, you can download the 28 Day NASR Subscription where you can find the airport table linking the airport name to the primary key found in the procedures name.
https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/NASR_Subscription/

Thank you so much, @wbeard52.
I have spent the afternoon digging into these. It is incredible how much data is in here, and getting the 28DaySub*, unzipping and exploring the CSV's was invaluable. However, even after digging through all of this, I still haven't made the connection to that original AL-582. The best connections I found were AP_BASE.csv and APT_BASE.csv, in which the SITE_NO (primary key?) for SEA-TAC is 26395. But no reference to this AL-582, 582, or 00582. A full text search has thousands of hits for 582, as a number, so I could be missing it. Any other thoughts?

Brilliant! Thank you for that follow up of the alnum="582".
I am curious if there is an effort to aggregate, present, and query this information in a tractable way.
Thank you again for your help and explanation!

AL numbers and the Office of Primary Responsibility (OPR, represented by the letters within parenthesis) are separate items. The AL number refers to the specific airfield. The idea was that if an airfield ever changed its name, identifier, or the name of the closest city, the AL number would remain the same. The first one was and continues to be Abilene Rgnl in TX. The OPR, on the other hand, is the office/agency responsible for that particular procedure. For example, the FAA may be the procedure designer for civil procedures, but the USAF may be the responsible organization for the high altitude procedures at the same airfield.
As indicated in 1, these organizations may be the FAA, an outside agency that develops the procedure that is then certified by the FAA (FAA-O), the US Army, the US Air Force, the US Space Force, or the US Navy. The DoD no longer shows AL numbers on charts, hence the part “Military procedures do not show an AL number, but do show the appropriate authority for the procedure, e.g., (USAF)”
I can’t help you with this one, but the naming convention typically includes the AL number, the approach type, and runway number.


text:
Could the reversers of a PW4000 on a 777 be deployed in-flight?
Could the thrust reversers accidentally be deployed during a flight? Here, I’m referring to the PW4000 series on a B777, where the engine is similar to the type involved in the crash of Lauda Air Flight 004.

A basic requirement of certification is the probability of any single point of failure that causes loss of the airframe (hazard level = catastrophic) must be better than 10 -9, or one in a billion.  A reverser deployment in flight would meet that level of hazard so system design has to meet that probability level.
In the case of Lauda Air, I would have to assume Boeing made a mistake in the system architecture that allowed a one in a billion event to happen "prematurely", and in fact they introduced a design change to get back to the required probability level.  In the case of the 777, or any other airliner, you have to assume the homework was done properly and the architecture meets the requirement until an event indicates otherwise.
Most of the time, gaps in design redundancy turn up during in-service events that are not as nasty, but that set off alarm bells at the OEM as potentially something more serious, and after a long process of analysis of risk and design, changes are implemented in the field by Airworthiness Directive.
It seems cold and calculating, but the whole thing is a numbers game where people with pointy hats with stars and crescents on them work out probabilities, of risk of death basically, using arcane methods like weibull analysis, to decide what to do and how soon to do it when design flaws turn up.  The transportation system couldn't function without it though.
Anyway, it's safe to say the risk of a reverser deployment in flight on a 777 is microscopic, but it's not zero, as nothing is in aviation.


text:
How do GLS avionics plot an entire accurate approach path?
I'm studying wireless navigation systems, especially GBAS. I have gone through some ICAO documents regarding GBAS. From what I have read, FAS data is included in Message Type 4. Closer examination of FAS data block tells that there is no block ID or sequence number which suggests that FAS data is not sent in chunks.
My question is, how does the on board equipment plot an entire accurate approach path? Since FAS data block has just the coordinates for LTP and FPAP.
I'm not a pilot so my understanding of operational details regarding GLS is pretty basic.

The best reference is the ICAO GBAS Guide.  Unfortunately, it doesn't have diagrams to help understand it.
The Final Approach Segment (FAS) is a geodesic path to the runway. It is horizontally aligned with the runway center line and has a glide path angle that descends to the Threshold Crossing Height (TCH) directly above the Landing Threshold Point (LTP). This can be seen in the following figure:

Source: SlideShare
All the necessary data is contained in the type 4 message as the ICAO table below shows:

Source: ICAO
There is one Type 4 message for each approach supported by the GBAS ground station.
The LTP/FTP latitude, longitude, and height are coded in the data block. The FPAP is coded as a delta Lat/Lon from the LTP/FTP. Horizontally, the FAS will pass through both of these points and thus be aligned with the runway center line.
The vertical component is defined by the Threshold Crossing Point (TCP which is the LTP vertically raised by the TCH) and the Glide Path Angle (GPA).

Thank! That helps a lot. So Type 4 messages defines the center line (LTP and FPAP) and the rest of the flight path until touchdown is dynamically calculated by the on-board equipment. Is this correct? Also, when the pilot enters the desired channel number, the equipment just receives 1 set of co-ordinates and TCH and GPA related data, right?

Right.  the LTP, FPAP, TCH, and GPA allow the GLS receiver to compute the flight path. The channel number does two things. First, the channel number is run through a hash to set the frequency for the VDB receiver to enable receiving the GBAS data. The receiver receives all the data broadcast from the ground station. The channel number is further used to select the appropriate Type 4 message from the data stream.


text:
Is MIL-PRF-5606 H flammable at 350 deg C?
Is MIL-PRF-5606 H flammable at 350 deg C?
Is it a flammable or combustible hyd oil?

Both Skydrol and 5606 will burn, though the original 5606 had a much lower flashpoint. However, there are modern derivatives of 5606 such as MIL-PRF-87257 that are within 10-15C of Skydrol's flashpoint and don't suffer the major drawbacks of Skydrol. The US military has switched to MIL-H-83282 which has a flash point, fire point, and spontaneous ignition temperature more than 200°F above 5606.
There are at least 5 flavors of Skydrol (and several for 5606) so it is a bit confusing to generalize "Skydrol" but Skydrol 500B has a flash point of 177 °C (350°F) compared to 5606 at 104°C(219°F). MIL-PRF-87257 very nearly matches Skydrol with a flashpoint of 170°C(350°F).
The two main drawbacks to Skydrol is it is extremely corrosive and much more harmful to human contact. 5606 and it's derivative MIL-PRF-87257 smell nicer and are less likely to attack rubber and plastic. One major disadvantage of 5606 is over time moisture will form condensate that oxidize aluminum tubing. This is one reason aircraft owners are told to regularly fly their aircraft; this prevents long term moisture bubbles eroding a spot in the aluminum line.

source - The US military considers the 5606 derivative MIL-PRF-87257 to more closely meet it's needs than Skydrol.

Absolutely. It likes to burn and in fact its flash point is very low, not that much above the boiling point of water.  The commercial aircraft industry and the military went to higher flash point phosphate ester fluid largely for this reason in spite of it's unpleasantness to handle.


text:
Angle of attack from velocity vector
I found an equation to calculate angle of attack based on the velocity vector in the body frame of the aircraft.
$\arctan(v_x/v_z) = \alpha$
1) Is this correct?
When I input in a $v_z$ approaching zero, the value approaches $\infty$ which means that angle of attack moving only in the x direction is 90 degrees since $\arctan(x)_{x\rightarrow \infty}= \pi/2$
2) Is there supposed to be an assumption that you never calculate Aoa of zero with this?
3) Am I misinterpreting what the velocities and angles represent?
Overall I am just a bit confused, because I kind of expected something that wouldn't mess up at level flight.

It is exactly the other way round:
$$ \alpha = \mathrm{arctan} \left( \frac{v_z}{v_x} \right) $$
You can simply derive it from the trigonometry in a triangle:

In this image the aircraft is moving to the right (along the arrow labelled v) and the $x$-axis is pointing along the aircraft body.
The resulting function looks like this:

For $ v_z = 0 $, you get $ \alpha = \arctan(0) = 0 $.
For $ v_x \to 0 $, you get $ \alpha \to \frac{\pi}{2} = 90^\circ $.

It looks like you are using a Vx and Vy defined relative to the horizon, not the aircraft body frame.  It looks like what you are describing is the climb or glide angle, not the angle-of-attack.  You can fix the first diagram by relabelling your V as Vx, and draw your Vz perpendicular to Vx and pointing generally downward (and a little forward) , and relabel your Vx as V.  This portrays the AoA of an aircraft in the illustrated pitch attitude in level flight ( i.e. horizontal trajectory). Of course the illustrated AoA would be rather extreme.

Anyway for a diagram redrawn this way, your comments about the correct formula are correct- it needs to be arctan (Vz/ Vx).  The comment about an angle-of-attack of 90 degrees seems a little odd, though technically true.

Reference for direction of x, y, and z in aircraft body frame: https://en.m.wikipedia.org/wiki/Flight_dynamics_(fixed-wing_aircraft)#Reference_frames

@quietflyer You are absolutely right! I fixed the sketch. Thanks :)

Also if Vz is zero, using Vz as defined in question (aircraft body frame), this means angle-of-attack is zero.  Says nothing about whether or not aircraft is in level flight.  So, this answer could use some improvement, even though it did give the correct formula for angle-of-attack.

You are welcome; looks like you were fixing as I was continuing to type more.  Anyway you are welcome.

I removed the false comments about level flight. That would only have been true in the incorrect reference frame...

This is only true without wind, of course...?

This is a good start building a backup AOA system that does not require a physical AOA sensor (that can break).  Just as human logic and laws allowed fewer lifeboats on the Titanic, the current disaster should lead to more redundancy.  This will work in wind because the triangle can be drawn based on IAS and rate of ascent/descent (if any). From there angle of nose to horizon is compared with direction of flight relative to horizon (with incidence of wing to nose, for you B-52 fans, added).  Note this can be done with existing instruments many times a second by computer.

@RobertDiGiovanni but think about what happens, say, if you deploy fuselaged- mounted spoilers or even wing - mounted spoilers, or for that matter just change power setting, all of which could in theory have no influence on angle-of-attack.  So ,  clearly for this vector diagram to relate to AoA, Vz must be relative to airmass not ground (relates to updrafts/downdrafts), and also must be measured in the exact direction drawn ( perpendicular to Vx), not vertically.  Also good point about diagram as drawn assuming zero incidence.  Vx also  must be relative to airmass (i.e.airspeed).

@quiet flyer there would be some error in what I proposed from updraft or downdraft, but it would be in the ball park and a good 3rd reference to compare.  It seems they need to make their AOA sensors a bit sturdier.  I'd think about putting an extra just outside my window where a rear view mirror would go in my car.


text:
What is the rate of climb of an airliner to reach cruise altitude?
Data from this question's answer states 2300 kg of fuel is used for takeoff/climb and 2500 kg of fuel per hour is used at cruise altitude.  Half hour idle descent burns 600 kg per hour (2% of total fuel use).
Using simple modeling of fuel consumption at glide, cruise, and climb (as a mirror image of glide) the "rule of thumb" fuel consumption for climb would be around 2x cruise based on a half hour descent at idle matching a half hour climb and a similar IAS and flap settings.
From all this, it is reasoned that airliners climb to cruise at around 1000 feet per minute.  How close are these numbers to actual climb rates of passenger airliners?

May be useful to understand the VS range used: What climb rates can the Airbus A320-200 achieve and which climb rates are commonly used for normal flight operations? and What are the climb rates during the different phases of flight of an A320? and also What is the vertical speed limit when altitude mode is engaged?

A lightly loaded B777 (115,00lbs of thrust per engine) can often have an initial climb rate of 5,000 feet per minute. Average climb rates are more like 2,000 - 3,000 feet per minute.

Thanks for the inputs, data from descent has engines  running (idle).  2000 feet per minute seems more like it.

Climb rates can also vary for other reasons.  A common one is noise abatement, where a steep initial climb is followed by a more gradual one.

At low altitudes, like below 10,000', the climb is much steeper than the descent, like a climb at 2,000 to 5,000 fpm & 250 knots, vs a descent at 1,500 fpm & 250 knots, or 1,200 fpm & 200 knots, or 800 fpm and approach speed (with some power being carried).
At high altitude, like optimum cruise, generally in the high 30's or FL 400/410, the reverse is true, with climb rate down to 1,000 fpm or less, but descent rate from altitude is easily 2,000 fpm or more depending on weight & descent speed.
On balance, the descent typically takes more time. Part of this is due to a greater prevalence of level segments on an arrival procedure than are found on departure procedures, but even in a case of uninterrupted climbs & descents, that generalization would still hold.
You're bound to have some descent segments that are level or close to it since you slow from ~280 knots to 250 at 10,000', and then from 250 back to approach speed later on (not necessarily all at once). Those segments trade about 10 knots per nm spent level & idle (until gear & flaps start coming out below ~200 knots); at climb power, acceleration happens much more rapidly than that.

Here's some figures used for "unreliable airspeed" situations for one of the largest current airliners - the pitch attitude and thrust settings result in the given IAS and V/S at different weights and altitudes. (disregard data within grey shaded cells):

During normal flight, the use of reduced/derated thrust would give correspondingly lower V/S values during climb and go-around.
[with thanks to Boeing]

A two-engined airliner will outclimb any WW II fighter aircraft at low level. Since the requirement to stay airborne with only one engine running means that the second one can fully be used for adding climb speed, a modern twin will climb at about 22 to 25 m/s at sea level. Typical sea level climb speeds in WW II rarely exceeded 20 m/s.

Yes, they have excess power, and might be most fuel efficient to nose up and climb at full thrust (for a shorter amount of time).  For a massive jet, one can see how that, without very carefully checking airspeed, can lead to stall issues.  I'm interested in bigger slats to help out.

@RobertDiGiovanni You want to keep L/D high, and slats won't help with that. In fact, the higher airspeed with clean configuration and best L/D produces the best climb speed for pure turbojets.

It will, but notice their angle of climb is all over the place because of variable mass.  I'm thinking hook the slats to the stickshaker.  The stabilator is in a world of downwash and turbulence at high AOA.

@RobertDiGiovanni Sounds like Auto Slats: see page 22 in this document: https://www.737ng.co.uk/B_NG-Flight_Controls.pdf


text:
Why we turn off anti-ice first then put on APU bleed after parking?
In A320 Standard Operation Procedure (Parking procedure), the order of parking procedure is anti- ice off then APU bleed as required. Is there any meaning for this order? Can’t we switch the order instead? If there is any relation based on system relationship, I would like to know.

Is A320 anti-ice electric - if so, then this'd be to reduce the load at switch over to ground power / APU off ...?  Covered at page 41 of the A320 normal procedures

@MrR No, it's not electric. I think the 787 is the only jet airliner that uses electric thermal anti-ice. All others use bleed air.

The "dupe" question is about Wing A/I; this question sounds like it's about Engine A/I. Is that not correct?

@RalphJ I thought Engine A/I is separate from the rest of the bleed system, but I can't find a diagram to prove it. Anyway, OP should probably clarify which anti ice system they mean.

The SOP calls for
ANTI-ICE ... OFF
APU BLEED pb-sw ... ON

the former covers both wing and engine anti-ice.
It is not allowed to use APU bleed for wing anti-icing, as defined in FCOM Limitations. (FCOM-LIM-APU-OPERATIONAL ENVELOPE)
As APU bleed has priority over engine bleeds the wing anti-ice valves have to be closed before APU bleed valve is opened.
For engine anti-icing the order does not really matter. Each engine uses its' own closed system for anti-icing with dedicated bleed valves.

Since each engine’s anti-ice is a local system, does that mean that if the engine shuts down for any reason and could be restarted later, there’ll be no anti-icing for that engine in the meantime? Has this ever caused a problem? (I doubt but curious)

Yes, since each engine anti-ices its own nacelle. Never heard it being a problem, but should engine fail in severe icing (especially if it flames out due ice) it is likely that it will not start again.


text:
Why is rare to see landings from East to West at the AJU airport?
Every day at the Aracaju - SE, Brazil Airport (IATA: AJU, ICAO: SBAR) planes take off from West to East and lands from East to West. But in rare occasions they will land from West to East. I think it might be related to the climate, as this is more common on rainy days.
Why is that?

Pilots prefer to take off and land heading into the wind whenever possible. This also makes ground traffic easier to manage, since it means planes can taxi to the runway at one end and taxi away at the other. So it'd be really unusual (though not unheard of) for an airport to have reciprocal takeoff and landing directions at the same time. So, when you say they land and take off, are you actually watching them land and take off?

This often is the case when the runway has a pronounced slope.

There's a mountain shelf just west of the airport, 70metres high at 1.7km west of the airport, climbing to 120 metres at 16km west.  https://en-gb.topographic-map.com/maps/ri5i/Aracaju/

Looking at the map of the airport, it appears they only have taxiways on the west side only!
Image copyright OpenStreetMap
Patterns may also be affected by wind direction, terrain, noise and airspace rules, but planes departing and landing in opposite directions may not be the most desirable arrangement.
An airplane landing west to east at AJU has to taxi down half the runway to get to the nearest off ramp.  Looking at the site from Google Maps, it does not seem to be very busy, so the way they do it may be fine for them.  Runway length is 7218 feet, elevation 26 feet, 12/30.  Apparently, in recent years, the runway was extended around 2000 feet, which accounts for its current configuration.


text:
How tight should my orbits be?
I'm flying VFR circuits at a towered aerodrome, and the circuit is quite busy. With traffic ahead of me to land, the tower calls on the radio and asks me to orbit on downwind. I know it's good airmanship to keep a neat orbit, centred over one point on the ground, but how tight should I make it?
A tight orbit takes up less space (I've known there to be three aircraft all orbiting on downwind at once), but at the same time, it seems like a waste of effort and fuel to be making tight turns the whole time when the point of orbiting is to kill time. A lazy orbit (at say rate 1) would kill time just as effectively while flying at a much more comfortable attitude - and more stable in windy conditions.

Have you practiced turns around a point? Its basically the same thing (which is why turns around a point are practiced at 1000', typical TPA). Usually when asked to make an orbit you would pick a point off the left/right wing and do a circle just like you practiced.

That's a lot of work. Better to pick a safe shallow bank angle, like 15 degrees and make a 360, and don't let yourself drift towards or away from the runway.

It sounds like "orbit" is UK-speak for making a 360-degree turn for spacing in the pattern.
I'm not sure what the custom is in the UK but in the US I was taught that you make a Rate One turn (3 degrees per second) for this, giving the tower two minutes between you and the aircraft in front of you (or the one on the ground they're trying to get rid of before you arrive).
The logic is that the maneuver is supposed to create spacing - flying a tighter circle takes less time, and thus creates less space between you and the aircraft in front of you. It also obviously requires more aggressive banking at low altitude compared to the relatively gentle bank required for a standard-rate turn at traffic pattern airspeeds, which as you noted will be easier to control in windy/gusty conditions.

'Orbit' is the ICAO language, '360' is FAA-speak

@DeltaLima The USA never met an international standard we didn't like ignoring!

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text:
Do the CAA's recent changes to medical requirements mean I wasted my time getting a medical?
I'm studying ab initio towards an EASA PPL. To be ready for my first solo, I obtained a class 2 medical certificate earlier this year. I had to take a day off work to do it and spend some cash that could have paid for flight time! Recently, the CAA has announced changes to the medical certificate requirements, aimed at reducing the need for private pilots to see an AME, but the announcement is not entirely clear to me.
Assuming these changes come into force before I first fly solo, could I have obtained an EASA PPL (and used all the privileges of that licence) without having obtained the class 2 medical certificate? If so, and assuming I don't intend to progress to a CPL or ATPL, is there anything else I need my certificate for, or any reason to renew it when that comes up in five years?

Just as a side note, I wish the US would get off its collective butts and pass third-class medical reform...

@RonBeyer I second that. I'm wanting to learn to fly, but even if I can manage to afford it, I'd have to stop taking some of my very beneficial meds. I'm sure as another pilot or person under my flight path you'd want me ON those meds rather than OFF of them.

No, I don't think so.  I believe there is a distinction between a UK PPL and an EASA PPL.  UK PPLs are defined purely by the CAA and only permit flying of aircraft outside the scope of the EASA licensing regime, such as some vintage and home-built aircraft.
The CAA proposal applies to the UK NPPL and PPL licenses not to the EASA PPL (with the exception that it may apply to pilots flying non-EASA aircraft in the UK only).
As it stands it is still necessary to have a class 2 medical to use the full privileges of an EASA PPL, although as footnote 1 says the CAA "aim to influence EASA in considering reviewing the medical requirements for EASA Private Pilot licence holders flying EASA aircraft".

I thought that at first, especially given I'd earlier heard the change was for the NPPL only. As I understand it, the only UK-specific thing is an NPPL. The linked site specifically calls out the NPPL separately, which suggests that what it calls a "UK PPL" just means an EASA PPL issued in the UK. That's why I'm confused!

@Nigel Harper is right - this only applies to UK PPLs, not EASA PPLs.

The system is a bit confusing - while the default for most people is an EASA PPL (and I would recommend going this route), the full set of licenses exists as national licenses in parallel:

LAPL (EASA) corresponds to NPPL (UK National)
PPL (EASA) -> PPL (UK National)
CPL (EASA) -> PPL (UK National)

With some rare exceptions, an EASA PPL is valid on UK non-EASA aircraft, but not the other way round.

I've just realised this deserves an answer of its own, but not to this question...

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text:
Why is it called "base" leg?
When flying a circuit, the leg after downwind and before final is called base. Where does this name come from?

Dan, please let me know what else you are looking in the answer.

@Farhan As you say, you've posted a good explanation or memory aid, but I was looking specifically for the origin of the term: how it came about, not just why the name makes sense.

Well, the first reason is the best one I could find.

Traffic pattern (circuit) phases are named so that they do not cause confusion1. I think of it as the leg which is taking me towards my landing/home base. (It is just a memory aid.)
However, the following reason is the best one which I found:

This leg represents the foundation for the final approach, that is,
  the base from which the final approach is initiated.

Another reason is as follows, although it is similar to a memory aid:

... base leg is called “base” because it is really the foundation of
  your landing (the “base” of a house is its foundation – and if it
  isn’t right, the whole house will never be right) – if the base leg
  isn’t right, your whole landing will suffer for it.

1: Although, upwind leg, crosswind leg and downwind leg relates with the wind direction too. But if wind is perpendicular to the runway, downwind leg is not actually downwind, but it is still called the downwind leg.

It comes from the French base, referring to the bottom of a triangle or rectangle.
If you view the circuit as a rectangle, the étape de base (the base leg) is the bottom step.


text:
When might an aerodrome contain a public right of way?
My textbook on air law says the following about Rule 41 of the Rules of the Air:-

A person shall not, without permission, go onto a part of an aerodrome provided for the use of aircraft. This applies to any part that is not a public right of way.

It seems unlikely that you would have a public right of way across the manoeuvring area or apron of an aerodrome. How common is this?

apart from Gibraltar, you mean? :P

Obviously, putting publically-accessible areas within an airport's apron, taxiways, or runway environments is normally avoided as much as possible. However, sometimes space constraints don't give you another option. As Federico mentioned in a comment, Gibraltar International Airport is a famous example of this. A major city street runs right through the center of the runway:

Gibraltar International Airport's runway with traffic on the street stopped for BA aircraft
In this case, the runway runs the entire width of the peninsula. Obviously, they had to allow traffic to pass back and forth from one side to the other somehow, so one of the main city streets passes right through the middle of the runway and they just stop traffic on the street when the runway is in use.
Of course, another way to solve this problem is to do what Nashville International Airport and Atlanta Hartsfield-Jackson International Airport (and probably several others) have done and just send the road through a tunnel under the runway. I'm not sure how feasible that would be at Gibraltar's low elevation, though (i.e. might have water problems in the tunnel.)

Murfreesboro Road passing underneath Runway 2C/20C, Nashville International Airport

Interstate 285 passing underneath Runway 10/28, Atlanta Hartsfield-Jackson International Airport
I would expect that the main reason where you have situations like the one in Gibraltar is probably economics. For low-traffic airports, it's a lot easier to just stop the traffic than to build a big tunnel capable of supporting a large aircraft. For higher-traffic airports (like Nashville and, especially, Atlanta,) though, the tunnel is required as there are flights landing or taking off constantly (not to mention the security and safety risks of having cars driving around within the airport.) According to its Wikipedia page, Gibraltar International only has about 10 flights per day (3,564 total in 2013,) so it's manageable to just close the road when the runway is in use. I expect other airports with these sorts of crossings will be similarly low-traffic airports (or, at least, a low-traffic part of the airport.)

I think it's less about the elevation and more about the terrain. The ground under most of this peninsula is solid rock.

@KeithS As far as I know, the same is true of Nashville. That's what dynamite is for. :) We frequently have to blast through rock to build roads and such here.

True. As far as I know, tunneling is by far the more popular option. Addison airport here in DFW is a Class D facility with a tunnel for Keller Springs Road running under its runway (it's fairly recent, like the last 10 years or so, and it's notable because the airport just kept right on running during construction). Underpasses for taxiways are so common it's not even worth mentioning specific examples; practically every airport with a center-terminal layout, or that's been expanded beyond its original land area, has at least one photo-op of a 747 passing over the top of a busy roadway.

@KeithS Yep. In fact, both of the pictured examples of runways over tunnels above also have other taxiways going over roads (the taxiway connecting 2R/20L to the terminal at Nashville and the one connecting 10/28 to the terminal at Atlanta.) Gibraltar apparently only has about 10 flights per day, so I guess they figured it wasn't worth the cost of building the runway over the road there.

Less busy than Gibraltar, but in the UK proper, Sumburgh in Shetland is an example of "road crossing the runway" on a relatively active airport - it even comes complete with level crossing gates, which are a startling thing to see on the road ahead when you know there's no railway!

My local aerodrome has a café underneath the control tower. To get to it, you have to go air-side and cross the main taxiway. There is no control on this - absolutely anybody can park up and walk over.
It's not strictly a public right of way, but I'm sure one exists somewhere.
With that said, I think you may be reading a little to much into it - the primary thing to take from that paragraph is that the Air Navigation Order can not override a public right of way.

Quite a number of airports in Switzerland have roads cross airports. This one is Alpnach Airport


text:
What should I look for when choosing a kneeboard?
There's a lot of variety in kneeboards. Some pilots fly with an improvised one: just a small clipboard with some scrap paper on, with a strap glued to the back. At the other extreme, fancy ones come with pen loops, pockets, and maybe even a fold-out area big enough to rest a map.
I'm not looking for a specific recommendation: I'm looking for how to choose. If I decide to make something homebrew, what should I bear in mind? If I buy a commercial product, which features are actually useful and which are "box features"?

You don't want something so big that it interferes with fully moving your control yoke/stick.  I have one that is about 1/2 sheet of paper in size (or about the size of an approach chart), that works good for me. Decent width of velcro strap to go around your leg.
Sportys.com has Aluminim VFR and IFR kneeboards, with good info printed right on it.  If you roll your own, they also have the same info available as a placard you could stick on.  The kneeboard and a few pieces of paper are all I've used.
I fly my own plane, so I can leave pens/pencils in places that are convenient for me.  If you are switching between planes, then maybe a kneeboard with holders for a pen or two would be handy also.
I also have a yoke mount clip that holds an approach chart. I found that trying to read a chart on my leg under the yoke was too difficult.  I may change to an ipad holder on the yoke as that seems to be the trend now.

You need to chose what works for you, and some trial and error may be pertinent here. Compared to the cost of flying knee boards are pretty cheap to cycle through. There are a few questions to answer that may be impacted by your training and the type of flying you are doing:
Am I an iPad Pilot? These days many people use iPads in the cockpit to replace paper charts. There are lots of options out there for iPad knee boards and with the scratch pad ability in most flying apps you can replace paper all together in the cockpit. If this is the way you fly you will want something sturdy that can hold the iPad in place. You may also want to consider a yoke mount.
Am I a paper pilot? If you like sectionals and a note pad there are various clip style ones out there. You can build one or buy it but I like the ones from the various major aviation suppliers as they tend to have some useful aviation numbers like weather minimums and those pesky tower light signals printed on them for reference. The military style ones tend to have a nice pen holder if thats what your after.
Do you want a side pocket? Be it clip or iPad style most knee boards I have seen are either single plate or dual in that they have a side pocket that hangs over (there are even some trifold ones out there I belive). The side is good for holding gum, extra headset batteries, a pen/stylus or an iPad cable (at least thats whats in mine).

Keep it small and simple.  People sell a lot of fancy kneeboards for use in cockpits and you'll quickly find that 90% of the features aren't going to be very helpful to you as a pilot.  Most are gimmicks and useless stuff.  Worse yet large awkward kneeboards or yoke mounts can interfere with one's ability to operate the flight controls effectively.  Just like gun aficionados will inevitably collect a drawer full of holsters, most pilots have a drawer full of old kneeboards with fancy features they saw in Sporty's and bought for 60 or so bucks but never quite worked as well as the basic $15 ASA kneeboard they inevitably ended up using.
My personal setup is a Hendrick's 9G Plus kneeboard which I use in conjunction with an iPad Mini 4 and ForeFlight.  It's a compact, functional, and simple - if somewhat pricey - kneeboard.  The iPad is contained in a Urban Assault Gear hard rubber case which the kneeboard can clip on to hold it in place.  It's by far the cleanest solution for using a kneeboard in the cockpit combined with an EFB.


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Does a line up and wait instruction clear me to backtrack the runway?
I had an interesting occurrence at the start of a recent flying lesson, at an aerodrome with ATC service. We were holding at A and completed our power checks. We hadn't requested nor been offered an intersection departure, and that is not a usual procedure at this aerodrome.
"G-AB ready for departure"
"G-AB via A line up and wait runway 23"
"Via A, line up and wait, runway 23, G-AB"
Following this, I entered the runway and turned to backtrack to the threshold. At this point my instructor said I should have turned the other way to line up at the intersection, because they didn't clear us to backtrack. Was he right to complain, or was I correct to use the full runway length?
Notes
A is only about 20 m from the runway threshold, and this runway is huge, so it makes little practical difference in this case.
At this aerodrome, they usually give LUAW instructions as "via [point], enter, backtrack, line up and wait runway 23". I checked CAP 413, and it doesn't mention "enter, backtrack, line up and wait" as phraseology, so I'd expect a clearance to LUAW entitles you to the whole runway unless you've already agreed an intersection departure. However, it's CAP 413 section 4.24 that introduces the "via A" phrase, and it has this to say:

When line-up will take place at a position other than for a full-length runway departure the intermediate 'Holding Point' designator shall be included in the line-up instruction. Controllers may include the runway 'Holding Point' designator in any other line-up instruction when considered necessary.

It gives an example, and the only other example with "via" is in the context of an intersection departure. As I said, at this aerodrome they usually include the "via"; maybe they just always consider it necessary. Is not saying "backtrack" here significant, even though it's not a standard part of a LUAW instruction?

If in doubt, ask the controller. For what it's worth, if I were the controller in this situation, I would not have expected you to backtrack. But I don't work in the UK, so your rules may be different.

Good question and I am interested in an authoritative answer. I don't have a reference but I seem to remember the FAA in the US gives explicit permission for back tracking - mainly because of the extra time involved. ATC uses the words "permission granted" or back taxiing "approved" which implies they have and enforce authority to do it.

I suspect if you had asked to backtaxi to use the full runway, tower would have come back with "Nxxxxx, cleared to backtaxi runway xx" or "Nxxxxx, negative, hold for traffic on base" (with the plane type called out), or perhaps "Nxxxxx, cleared to backtaxi runway xx, expedite for traffic on base (or final)" with the plane type called out". And you would read  back the clearance, and then backtaxi or wait.  Otherwise you might expect to be scolded by the tower, especially if you caused a go-around situation for another plane.

If you can put the airport diagram it would be more clear. Everybody is trying to answer as if it’s a intersection takeoff, but your’s is definitely not.

Your instructor was correct. According to the CAA Radiotelephony Manual[pdf], since the clearance you received included "via A" your clearance was not for a full length takeoff.
From the Radiotelephony Manual, chapter 4:

That's the same section I quoted in the question, and it doesn't clearly imply what you claim. It says that if it's an intersection departure, they must say "via A", and in any other line-up instruction, they may say "via A".

But in your question you indicated that they did say "via A," so that indicates that is was an intersection departure.

I would say that backtrack, takeoff, holding on the runway, and entering the runway for any other reason (for example to cross) are distinct actions that require readback.
ICAO's Annex 11 (here reproduced from Appendix A of their Manual of the Prevention of Runway Incursions) regards all these items to require specific readbacks as clearances or instructions, and itemises them individually. The logic being - a clearance to take off is not entailed by a clearance to enter the runway, or to line up, or do anything else. Why should a clearance to backtrack be so thought of?
In Australia (my jurisdiction) this para from Annex 11 is reproduced pretty much verbatim in our own AIP and MATS.
I have seen in Australian Pilot Guides (advisory documents) that backtrack approval is specifically required, though I haven't seen that replicated in the AIP itself. A cursory glance through the CARS etc hasn't turned up anything either. The ATC Manual Of Air Traffic Services in Australia, however, says specifically as 12.3.2.8

Backtrack clearance
When the pilot has requested backtrack with the 'READY' or 'REQUEST LINE UP' report, give
  the instruction to 'BACKTRACK RUNWAY (number)' before the line up instruction.
Note: An ATC clearance to line up does not authorise the pilot to
  backtrack on the runway.

And at 12.3.2.9

When entry to the runway will be from a position that is not adjacent
  to the runway threshold and a pilot reports 'READY' without requesting
  or accepting an intersection departure, or requesting backtrack,
  ascertain the pilot's intentions prior to authorising entry to the
  runway.

Given this, if we were able to extrapolate something similar to your procedure (and most of our procedures are quite like yours and ICAO on things like runway separation, we have conditional clearances etc and use standard phraseologies), I would say what SHOULD have happened in this scenario is that you should not have initiated backtrack on the runway without specifically hearing and reading back the instruction to backtrack (a takeoff is not a line up, and neither of those are a backtrack), but that ATC should also have queried your intentions because you had neither requested a backtrack nor an intersection departure.
I can't speak certainly for UK ops, but I'd say we're probably fairly close. We even just adopted your "flight level two hundred" phraseology! :D
Also, if you think about things like runway sep and flow to the runway, it makes sense why it would make a material difference to ATS if you needed to backtrack or could depart via the intersection, and why they would want to know before letting you into the runway. Flying GA out of a smaller airport it would matter, but it's easy to imagine at busy airports with maybe a couple of minutes between subsequent arrivals it makes all the difference in the world.

Your source is really good and unambiguous. If it were for my locale I would accept your answer for sure. I don't accept your other reasoning though. A clearance to take off or line up does imply a clearance enter the runway (though sometimes controllers do say that explicitly), so I don't buy them being "separate actions". Also, while I agree that intersection departures are useful for operations, that doesn't mean I should expect one without having talked about it. "Land after" and "behind" clearances are similarly useful but they still need to be explicitly agreed!

Well, I can certainly see how you would be leery of accepting because of jurisdiction (though we're pretty closely aligned as far as a lot of this most fundamental ICAO stuff goes), but I would disagree with the rest of your reasoning. Yes, a clearance to t/o, backtrack, cross etc DOES include a clearance to enter the runway (by necessity), but that doesn't imply the reverse is also true. If I've crossing a runway, that does not allow me to stop on the runway, which a line up does. They (cross, backtrack, takeoff, line up) are distinct in ICAO for good reason.

You were correct in using full length. When intersection departure is initiated by ATC it shall be accepted by the pilot. As ATC did not mention intersection depature, which also means you did not accept a departure from Alpha, the clearance from ATC is for full length. Also take note that the aerodrome your using has to comply with conditions of 6.5.2.2 to 6.5.2.6 in the regulations below in order to be able to use intersection dep.
Below you can see the regulations. This is from the current editon ICAO DOC 7030 (Regional Supplementary Procedures).

6.5.2    Intersection take-off
6.5.2.1 An aircraft may be cleared to depart from a published intersection take-off position upon request of the pilot, or if
initiated by ATC and accepted by the pilot, provided that all of
the conditions of 6.5.2.2 to 6.5.2.6 are met.
6.5.2.2 The declared distances for each published intersection take-off position shall consist of the following:  a) take-off run
available (TORA) from the intersection take-off position; b) take-off
distance available (TODA) from the intersection take-off position; and
c) accelerate-stop distance available (ASDA) from the intersection
take-off position. 1/11/13 No. 8  EUR  6-4 Regional Supplementary
Procedures
6.5.2.3 The reference point from which the runway declared distances for a published intersection take-off position are measured shall be
in accordance with the relevant provisions in the Air Navigation Plan
— European Region, Volume II — FASID (Doc 7754), Part III — AOP.
6.5.2.4 Declared distances for an intersection take-off position shall be published in the relevant AIP, clearly distinguishable from full
runway declared distances.
6.5.2.5 Information on the TORA from the intersection shall be issued when requested by an aircraft or whenever deemed necessary by the
controller.
6.5.2.6 Signs shall be in accordance with Annex 14, Volume I.

Christian Speichert,
ATCO.

Disagree. Sure, the pilot has to accept the shorter distance, but it is up to the pilot to make the controller aware if backtrack is required.

The pilot should request clarification if unsure, that’s true. But it’s also up to the controller to issue the proper clearance in the first place. Which in this case should have been “G-AB, via (Alpha and) RWY 05, line up and wait RWY 23”. As the clearance here was "only" missing the “via RWY 05” I can understand why the pilot would assume that he is cleared for full length. In this case the intersection was not far from threshold, but in another you could have a significantly reduced TODA.

If proper phraseology is not used by the controller an assumption that the pilot should accept an increase in risk due to reduced TODA is unreasonable in my view.
So, I agree Mr. Hougaard, the pilot should check that he is cleared to taxi on the RWY if unsure or given an inadequate clearance. But in aviation, sometimes, clearances are not always uttered in accordance with regulations and are based on an assumption of mutual understanding. In this case, my opinion is, that the more correct action was to proceed with the taxi for full length rather than set up for intersection departure.

Also, and this is not known in this instance, unless the intersection has published distances it is not allowed to be used for departure. In such an instance the controller would not only be breaking the rules if the pilot would line up and depart form intersection A, he would also “force” the pilot to break the rules. (I use the term “force” loosely as it is of course the responsibility of the PIC to not accept any clearance blindly)


text:
Is there a maximum airfield elevation in which a Cessna 172P can operate?
The title says it all: is there a maximum airfield elevation in which a Cessna 172P can operate? Or a maximum density altitude at which take off shouldn't be considered?

There are two questions here. The first can be answered, approximately, if you know the aircraft weight and runway length. The second involves a judgement call taking into account other factors such as pilot experience, climb requirements, and other weather issues. An easy but very incomplete answer would be just to look at the highest density altitude listed in the takeoff performance tables.

You should look in the POH for your specific aircraft (because it may have had modifications to it which would make it different from a "standard" aircraft) and see what it says.
The 172P POH that I found online contains no maximum airport elevation for takeoff, and the Type Certificate Data Sheet (TCDS) doesn't either.
Therefore, you can only go by the performance charts in the POH.  According to the POH that I found above, assuming that you have enough runway available and can out climb any obstacles (big assumption, you need to make sure of this), you can takeoff at a pressure altitude of up to 8,000 ft. other than in cases where the airplane is very heavy and it is hot, in which case it will be restricted further.
This doesn't mean that the aircraft is not capable of taking off at a higher pressure/density altitude however, and if you have the need to do so then I would recommend contacting the manufacturer directly to see if they have any engineering data available for your situation (often they do but don't publish it; there may or may not be a fee).

I don't know of a maximum airfield elevation, though I suppose the airplane's service ceiling would qualify as an answer to this question.  In regards to the second question, that is largely going to depend on the airfield elevation, runway length, climb gradients needed for obstacle clearance, and ambient atmospheric conditions.
These questions would have to be answered during your preflight performance calculations.  You're going to have to consult the pilots operating handbook and cross reference the performance charts listed for both the takeoff distance and climb performance with information in the airport/facilities directory for the elevation, runway length, and departure procedures plus information from your weather briefing.
As an example calculation - and I'm using the CE-172S POH for this - let's say you are departing Lake Co Airport KLXV in Leadville, CO flying to Central Colorado Regional KAEJ.  AWOS at KLXV reports Winds 220 deg at 7 kts with good visibility, temperature 21deg C/69deg F, local altimeter is 30.47" Hg, and Density Altitude is 12,262 ft.  In these conditions, the POH doesn't even report a takeoff distance above and 8000 ft pressure altitude.  The aircraft's service ceiling is approx 12,500 ft, meaning even if the pilot could somehow get airborne and fight his way out of the ground effect, he would still be able to climb at an anemic 100 FPM max, unacceptable for any kind of maneuvering and obstacle clearance.  It would be an extremely hazardous exercise to attempt a takeoff at this airport under these conditions.
Another example:  let's say we're are departing Ogden-Hinckley KOGD in Ogden, UT on an IFR flight plan to Fanning Field KIDA in Idaho Falls, ID.  KOGD ATIS reports winds 129deg at 6 kts, temp 30deg C/86deg F, altimeter 29.98" Hg., and a density altitude of 7,101 feet.  The winds favor RWY 16, which is 5,195 feet in length.  Assuming we are fully loaded at 2550lbs, using the performance chart for the takeoff roll, at a pressure altitude of 8000 ft (to be on the safe side) and temp of 15deg C (remember, this is what density altitude represents), we find a needed short field takeoff roll, flaps 10 deg, paved level runway of 1995 ft in still air.  The POH suggest reducing takeoff roll by 10% for every 9 kts of headwind.  Here we have a ~4 kt headwind component, so we can extrapolate a takeoff roll of 1907 ft in these conditions.  I like to use an additional 20% safety margain, which give us a final takeoff roll of 2288 ft.  RWY 16 at KOGD is 5,195ft with no obstacle clearance procedures required.  Your maximum rate of climb would be about 410 FPM as interpolated from the charts - pretty lackluster and again using a 20% margin of safety give 328 FPM this becomes even slimmer.  This flight would not be recommended if you had terrain or obstacles to quickly climb over, and the routes to our destination require at least a 10,000ft MEA enroute.  Instrument flight would not be recommended today doe to lack of aircraft performance for the required route.  A VFR flight up through the valleys by Logan, Downing and Preston might be possible however.


text:
How much rudder input does a Cessna 172 require during the take off roll?
I am part of an open-source project developing a simulation of a Cessna 172P. We are tweaking our flight dynamic model at the moment and we are looking for feedback from people with real life experience on the 172. In particular, we would like to know how much rudder input does this aircraft require during a take off roll (with no winds) in order to keep it centred on the runway.

I don't think you can get a numeric answer, short of putting a force sensor on the rudder pedals.  The only  answer I could give is "enough".  You do it by feel, not by numbers.

@jamesqf Thanks for the quick reply. I know that getting a numeric response is impossible, but we are interested at least in some vague figures. For instance, supposing 100% would be full rudder, would you estimate that you must apply nearly no pedal at all (5%) or would a much larger figure (30%) be more accurate? That is, in your personal opinion, would you estimate that you apply extremely little or a representative amount of rudder? Many thanks.

Shouldn't your team be flying the 172 pretty much everyday?   Reminds me of a programmer friend who worked at an Amazon warehouse one holiday, there was lots of automation to help pickers do their job, but it was incompetent, like the developers had never seen an Amazon warehouse, and so pickers were badly underused and wasted time on an industrial scale.  I'd have forced the Dev team to work in the warehouse 1 day a week.  And the holiday rush.  So get flying folks!

@Harper That's quite harsh. We are a team of volunteers who work on this open source project on our free time. Some of us do indeed have a little experience flying but not necessarily on the 172 and not necessarily hundred of hours. We always try to get feedback from real pilots and also invite them to test our aircraft (it's a free open source simulator, after all). Lately we received a lot of different opinions regarding whether the P-factor and propwash effects are too strong in our flight dynamic model and I was hoping to be able to get a feel from more experienced people in this platform.

As for the 'get flying folks', trust me when I say that I would love nothing more than to get flying lessons but unfortunately I simply don't have the money for that at all. I have been obsessed with having flying lessons since I was a kid but I simply cannot afford it.

What's harsh is that you're trying to write a simulator for something you have never experienced for yourself. Enthusiasm is grand, but know your limits and know when you need help.  Get some actual 172 flyers NDA'd in and on your design team, and then listen to them.

@Harper I appreciate you taking your time to reply but I don't appreciate the attitude at all. On top of that you are not answering the question nor touching it all. Let's just leave at this.

One thing that makes this difficult is that PC-level sim aircraft controls aren't flown like real aircraft controls.  With the usual PC joystick, you fly by stick position.  But with a light aircraft, you fly by control force rather than by control position.

@gilberto.agostinho.f Goodwill alone is not enough. Imagine a reverse case: you're a pilot and you've started writing a simulator - but you have no idea about programming at all so you come asking on stackoverflow on how are functions written. You'd get same answer - sent to "programming for beginners" course. Harper is 100% right on this: First you need to know what you want to achieve, then start going there, not the other way around. Most of programming is getting the requirements right.

@Agent_L I fail to see where I have been asking people's opinion on my goodwill in my question. This got absurdly out of topic and your opinions on our sim are frankly out of touch with how things work. First, this is a sim that exists for over 20 years and has been created by pilots and programmers from all sorts of backgrounds. The original FDM of the 172 has also been created by a highly capable pilot AND programmer. Given that I am not a real life pilot, my volunteering does not include FDM feedback as I completely lack that knowledge (I work mainly with textures and sounds).

The person currently improving the FDM has flying  experience but not in a 172. He is simply tweaking the FDM in order to simulate effects that we can not only read about but which are reported to us by pilots. But all modifications are also tested by pilots. The only reason I asked a question here is, as I pointed out, we had some conflicting information from people flying the 172 and I was hoping to find someone with large experience in this aircraft to give his two cents. All I was looking for was 'I have 300h in the 172 and it requires very little rudder' or something like this.

@Harper OP is working on an open-source project. There should be no need for a non-disclosure agreement of any kind because everything will be out there in public eventually anyway, and might be already depending on the exact development model used.

I am a software engineer and a soon to be commercial pilot (currently PPL with IR and 200 hours) . Here's my advice. Implement the rudder input to be programmable/configurable and then have a pilot test it, tweak the programmable parameters until they say the feel is just right. Make sure you can have a way to use a different coefficient during different stages of takeoff roll and climb as your rudder input will vary with speed/power setting

Of all the functionality I would want in a simulator, graphics, instrumentation, features, realistic flight performance, etc. accuracy in accounting for a slight tendency to pull left on takeoff roll would be one of my least concerns.  About as important as accounting for torque steer of a 200HP front wheel drive car when accelerating in a driving simulator.  Or attempting to calculate the angle of forearm deflection due to recoil in a 175lb soldier when firing a 9mm Beretta in a war game.  Make it need "just a little right rudder" and call it good enough. Or, don't bother.  Just my opinion...

With several hundred hours logged on multiple variants of the 172, I would give the relative answer of ‘not much’.  In my experience a C-172 tracks pretty straight with only slight right rudder pressure needed on the ground roll.  It is much less than what is required for a C-182, 206, 210 or other high performance single engine Cessnas and much less that a lot of tailwheel airplanes I’ve flown.
It seems like in a 172 when you are brakes off and rolling, I usually rest my heels on the cockpit floor and apply a slight pressure on the base of the right rudder pedal with the ball of my right foot.  It is necessary as the plane will waltz to the left during the takeoff roll if you don’t.  But the force applied and the deflection of the right rudder pedal is light and limited, if you do it right.
A recommendation might be to send a developer down to a local flight school operating the C-172 and arrange to practice takeoffs and landings with a CFI so they can get an empirical sense for what rudder input is needed on a takeoff roll.

"Not much", true, yet when I first flew C172 after hours of initial training in C152, I thought: wow! that's a lot of rudder!

@Zeus I had the same experience moving from a C172 to a C182 to get my high-perf endorsement. One hour of showing the CFI that I could use enough rudder to keep the plane straight, and done.

If you want to feel really strong left turning tendencies on the takeoff roll, try flying SR-22s or high powered Lancairs.  They’ll give your right leg a good workout!

Wayne Conrad made a very important point in the comments which deserves serious consideration. Namely, flying is done by force, not by position. 'Apply that much pressure' rather than 'move by that much'. (This, in fact, applies to most well-designed controls of such kind, for example, brakes in your car).
This is beneficial for dynamic control because we have a better force feedback in our muscles than a position feedback.
But this raises two problems for simulation. First, a certain amount of pressure (which normally provides a certain amount of net effect) translates to different amount of movement in different conditions, particularly at different speeds.
For takeoff roll this is even more complicated because the nose wheel works proportionally to position (and even this is not quite true because the linkages have springs), while the rudder works proportionally to force, and one gives way to another during the roll. In practice, I'd say, you need to gradually increase the pressure while the amount of actual deflection reduces!
Second, all stock PC gaming controls work by position and cannot re-create a realistic force feedback. So unless you are building a simulator with specialised control loading, you can give up any hope of creating a simulator that feels even remotely correct at the controls. This is, perhaps, the source of much disagreement between pilots when they are asked to evaluate such a simulator.
For this reason, it may be better not to pursue 'true' control inputs for a PC simulator. It may be unflyable. For example, if I say that C172 requires about 10% or rudder deflection during takeoff (which is not too far from the truth) and you implement it thusly, I bet I myself would find it difficult to keep the model on the centreline. The truth is, what I remember is not the 10% deflection but rather (say) a couple of kg of force that is required. Yet this force will push most PC pedals to the limit, or at least much farther than 10%. And doing 10% corrections would be difficult, because the force required is so light. So in the end it may feel more real, or at least more flyable, if you make it 50% rather than the 'true' 10%: it will be closer to the true force, which is far more important.
But then, how do you simulate full deflection? Well, you cheat. You add significant non-linearities (S-curves) to the controls, you treat on-the-ground conditions differently to flight, etc. This may sound anathema, but it may be a better compromise and may create a better simulator.

Thank you for turning my comment into an answer, and much better than I could have.